New flexible neutral particle beam system for improved control of fusion energy

Researchers working at the DIII-D National Fusion Facility at General Atomics (GA), in collaboration with scientists from University of California-Irvine and Princeton Plasma Physics Laboratory, have created an important new tool for controlling energy-producing plasma in fusion devices. This work will be published in the January 2017 edition of Nuclear Fusion.

The fusion reactor is a device that confines the plasma in a closed space to maintain a sustained nuclear fusion reaction. Tokamak is the most common magnetic confinement device and uses magnetic fields to confine the plasma. Powerful neutral particle beams heat plasma to temperatures hotter than Sun.

Up to now, these neutral beam injectors accelerate particles through fixed high voltage (~90,000V). Experiments have shown that the high velocity of the resulting beam particles can produce or amplify electromagnetic plasma waves. These waves can kick those particles out of the plasma and cause them to smash into the walls of the reactor.

Therefore, high beam power is necessary to produce high plasma temperatures, but unfortunately the beam particle loss reduces the plasma temperature and can lead to costly damage along the tokamak walls.

The new designed variable voltage beams are a solution to these issues, since varying the beam voltage in real-time allows to minimize wave-particle interactions and limit the interference. As a result, this solution allows the beam particle voltage to later increase to maximum levels, thereby improving magnetic fusion.

Next steps will consist to extend this new technique to an even wider range of plasmas, taking advantages of the control and diagnostic opportunities it provides.